Purpose

• Understand the properties and behavior of 

liquefied natural gas (LNG)

• Identify LNG fuel tenders, locomotives, tank 

cars, and intermodal portable tank cars

• Understand potential chemical, cryogenic, and 

flammability hazards

• Execute the basics of LNG emergency response

Properties and behavior of LNG 

upon release

• LNG is a cryogenic liquid formed from natural 

gas (NG) cooled to a very low temperature of 

–260 °F (-162 °C) at atmospheric pressure.

• When heat is added to LNG at atmospheric 

pressure, it boils and is converted into NG.

• LNG is colorless, odorless, and non-toxic.

• The volume ratio of LNG at –260 °F to 

atmospheric pressure NG at 70 °F is 1:600.

• LNG or vapor leakage is detected using only 

certified instrumentation, such as hydrocarbon 

concentration sensors.

• LNG is stored in insulated, thermos-like double

-walled tanks.

• LNG leaks and spills lead to the formation of a 

cold, ground-hugging, white, visible natural 

gas cloud, which is visible due to water vapor 

from the atmosphere condensing into the 

cloud as a fog. 

More Information

For more information on emergency response 

guidance:

• BP Process Safety Series: LNG Fire Protection 

& Emergency Response, Institution of 

Chemical Engineers, 2007

• Emergency Response Guidebook, U.S. 

Department of Transportation, 2012

Emergency 

Responder 

Guidance

Liquefied Natural 

Gas (LNG)
Identification of LNG 

tenders and tank cars

• A fuel tender will always be coupled to a 

locomotive. It may have decals indicating 

that the tank content is “Liquefied Natural 

Gas.”

• An LNG tank car or intermodal portable tank 

will have a placard with “UN 1972” and will 

be marked ‘”Refrigerated Methane Liquid.”

Potential hazards — respiratory, 

cryogenic, and flammability

• Chemical hazards

– The rapid evaporation of released LNG into 

vapor can displace air and can cause 

asphyxiating conditions in confined spaces.

– If only a small amount of LNG is released, it 

will evaporate and the vapors generated 

will quickly dissipate in the atmosphere.

• Cryogenic hazards

– Contact with cryogenic liquid, cold surfaces, 

or cold vapor can cause burns, also known 

as cold burns. 

– Breathing cold vapors can damage lung 

tissue.

– LNG contact with materials, such as carbon 

steel, can lead to material embrittlement.

• Flammability hazards

– The natural gas cloud formed by LNG 

vaporization and mixed with air will ignite 

only when the gas-air mixtures is in 

concentrations between 5% – 15% by 

volume.

– If a vapor cloud ignites, a flash fire will form 

and propagate (upwind) to the source of 

vapor. Occasionally, for short distances 

downwind of ignition point, the cloud may 

propagate a flash fire.

– Natural gas flames burn cleaner and more 

luminously that gasoline flames of the 

same size.

– LNG vapor mixed with air in the 

flammability range is not explosive in 

unconfined conditions. 

Basics of LNG emergency response

• Stay upwind. Keep unauthorized personnel 

away.

• Do not enter an LNG cloud.

• Look for recognizable signs of escaping gas 

(sound and/or white cloud). Escaping gas is 

odorless.

• Eliminate ignition sources (no smoking, 

flares, sparks, or flames in the immediate 

area).

• Use thermal protective clothing and gloves in 

addition to respiratory protection.

• Initiate emergency shutdown functions.

• Stop the release if possible and safe to do so.

• Do not direct water at spill or source of leak.

• Verify whether cab sensor/detector has been 

activated in the locomotive if unsure about 

whether there is a leak.

Contact Us

Dr. Phani Raj

General Engineer

Hazardous Material Division

(202) 493-6306

Phani.Raj@dot.gov

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